The invention relates to shapemetering. A process and apparatus are disclosed for visual automatic monitoring and continuous resultant correction of the profile and surface flatness of rolled strip, metal or otherwise, and in particular for metals which are rolled and subsequently rewound.
Whilst the disclosure is directed principally toward mills utilized for rolling metal strip, the application clearly embraces other types of plant for the forming of non-metallic strip materials; thus, notwithstanding reference is made to rolled metal strip throughout the specification for ease of description, such reference in no sense limits the scope of the invention.
Detection of the shape of metal strip, that is, of its profile and flatness, is of vital importance in rolling especially since the high production tempos now reached with modern methods dictate that such an operation can no longer be committed to inspection and manual adjustment on the part of mill operators.
In FIG. 1, the schematic representation of a rolling mill, given as an example, illustrates a metal strip 1, a pair of work rolls 2 and a relative pair of back-up rolls 3. The rolled strip is rewound onto a recoiler 4.
The train of rolls, so-called, may also incorporate idle and tensioning rolls such as those denoted 32 in FIG. 1 over which the strip 1 is run in order to ensure the best possible distribution of tension and constant alignment on arrival at the recoiler 4.
During rolling, the surface of the strip 1 may appear perfectly flat and free from faults or unevenness, to the naked eye; this notwithstanding, the tension to which the strip is subject, and its high speed through the mill rolls (often hundreds of meters per minute), are such that visual inspection alone cannot detect these defects, especially where small and/or localized.
Single faults and general unevenness may be manifested in different ways, continuously or localized, occurring across the main body of the strip or near the edges alone, and may be of diverse origin. Such defects in rolled metal strip 1 can be attributable to errors in `tilt` and `crown` of the mill rolls 2 and 3, or more often, to the lack of proper distribution of cooling on these rolls (usually effected by spraying with special coolants). Diverse tilt and bending components can result in localized hot-spots in the surface of the strip 1 by reason of differential roll expansion, and differences in gauge across the width of the strip cause greater heating where reduction is greatest.
The need therefore exists for selective cooling along the longitudinal dimension of the rolls 2 and 3 that will take account of such deviations and diminish the effects produced thereby, thereby improving the shape of the strip as manifested on exit from the mill rolls.
The faults and unevenness in question are manifested, in practice, by surface drift which produces localized or continuous variation in the running tension of the rolled strip, hence in mechanical pressure which the strip will exert on a surface disposed beneath and transversely tangential thereto. These parameters are duly exploited in the prior art shapemetering devices currently in use, which are installed between the train of mill rolls 2 and 3 and the recoiler 4. Such prior art devices are designed, in essence, to detect a given number of increments in the width of the strip for any variation in pressure exerted by the metal in each such increment, by way of sensing elements that make contact with the running surface of the strip.
In one embodiment of such a prior art device, a number of rotors mounted adjacent to one another and rotatable on a stationary transverse shaft have respective cylindrical cavities filled with fluid which is pressurized to a constant value. Measurement of the variations in strip tension is achieved by detecting the difference in pressure of the fluid, occasioned by positive or negative shift in the strip tension transmitted to each rotor, between two opposite set points. Transducers are used to relay the detected information to a CPU which, having acknowledged and processed the input data in the prescribed manner, relays control signals which actuate appropriate corrective media.
Notwithstanding such a method is tolerably effective, the rotor device involves notably complex construction, by reason of its comprising fixed and moving parts and pressurized-fluid seals, and of its being characterized by tight tolerance margins in embodiment; the device is thus invested with a certain structural inertia which in turn has a limiting influence on sensitivity, and which, given the complexity of the control system, does not permit of real time corrective action via the media utilized for rectifying error. These design drawbacks are compounded further by a requirement for continual servicing and verification of the device's efficient operation, and by a marked energy consumption, which in turn signifies somewhat high outlay and running costs.